Rohde & Schwarz R&S UPP, User Manual

Page: 432 / 938

Instrument Functions
R&S
®
UPP
416 User Manual 1411.1055.32 ─ 10
Freq Limit
RMS value calculation on the basis of the FFT bins between frequency marks
"deactivated" The frequency limits for calculating the RMS value from the FFT bins
is based on the Start and Stop values of the FFT (shown but not
accessible), i.e. the calculation is broadband-based.
"activated" The bandwidth for calculating the RMS value from the FFT bins can
be limited. In the two following fields, the lower and upper band limits
are indicated – as for the THD+N measurement.
When the bandwidth is reduced, the device only looks for the fre-
quency in this range when in "Meas Time" = "Prec" measuring mode.
If the frequency of the broadband signal is to be determined, either
the time for measuring the frequency must be set to "Meas Time" =
"Fast" or the bandwidth limitation must be disabled.
When the AC coupling is enabled (or "DC-Suppress" in the digital
range), the RMS calculation starts above the DC bell curve. When the
Window function is disabled, i.e. "Window" = "Rectangular", only the
DC bin (otherwise the first 6 bins) are suppressed. Thus, with DC
suppression the actual lower frequency limit depends on the Window
function, which means that the FFT size may be larger than the value
selected by the user.
Applying band limits that have been limited with both of the following
parameter fields to the limits of the x
‑
axis in the FFT graphic would
not be desirable in most cases, and is not done.
Remote command:
SENSe[1]:FREQuency:LIMit
on page 762
Freq Lim Low
Lower band limit for RMS value calculation based on the FFT bins.
Remote command:
SENSe[1]:FREQuency:LIMit:LOWer
on page 760
Freq Lim Upp
Upper band limit for RMS value calculation based on the FFT bins.
Remote command:
SENSe[1]:FREQuency:LIMit:UPPer
on page 760
FFT Analysis